encephalisation

/EH1 N S EH1 F AH0 L AH0 S EY1 SH AH0 N/
noun
  1. 1

    The amount of brain mass exceeding that related to an animal's total body mass.

Source: https://en.wiktionary.org/wiki/encephalisation, https://en.wiktionary.org/wiki/encephalization